Ocean Radar

Between 2007 and 2012 the Ocean Radar facility installed 12 HF radars, arranged in 6 pairs. In

collaboration with the IMOS Data Management team and local caretakers at the remote sites, the

Ocean Radar Facility, located now in Perth, operates maintains and processes data from these

radars to provide surface current measurements that

are available in real-time on the Australian Ocean Data

Network (AODN) Portal. In addition to currents, wave

and wind measurements are also now available on the

Australian Ocean Data Network (AODN) Portal. HF Radar

data can also be seen together with satellite, Argo floats,

and other data on the IMOS OceanCurrent website.

The Australian Coastal Ocean Radar Network includes

the two main types of ocean surface radars that are being

used around the world. They are the Phased Array genre

(WERA), manufactured in Germany, and the Direction

Finding genre (SeaSonde), manufactured in California

(US).

Technical summary

Instrument and Data

Ocean Radar

In a phased array a narrow beam is formed by adding phase offsets to antenna elements in the

phased array. The width of the beam is determined (inversely) by the length of the antenna array.

The beam formation is fundamentally robust and the azimuthal resolution of fine structure in the

surface currents is determined by the antenna beam width.

The phased array performs particularly well when the surface current field is complex, with eddies,

jets, and fronts. Also, with phased array methods, the second-order echoes may be used to determine

directional wave spectra at ranges up to about half the range for surface currents. The long-range

systems, operating at around 8-9 MHz maps surface currents to ranges of up to 200 km, and directional

wave spectra up to 100 km. At higher operating frequencies the current values are more accurate,

but the operating range is less. The phased array HF ocean radar is robust and has high precision.

Technical summary

Phase Array

Direction Finding

In direction finding ocean radars the direction of arrival of a signal is determined by the amplitude

response of orthogonal loop antennas. The small antenna footprint is the most desirable feature.

The direction finding procedure is critically dependent on the calibration of the polar patterns of

the antennas. For simple flow patterns, the radial components of surface current are accurately

determined. Direction-finding systems generally have wider azimuthal coverage than phased array

radars. The long-range systems, operating in the 4-5 MHz band, is capable of mapping surface

currents up to 200 km. Directional wave spectra can be determined in waters close to each of the

stations. The direction finding HF ocean radar is reliable and is particularly good for large-scale

steady flows.

Ocean Radar

The basic current data provided by either type of radar is a radial current – i.e. the component

of the ocean current along the direction from the radar site to the measurement position. This is

obtained from the frequency shift of the first order peaks in the Doppler spectrum with respect from

its position as predicted by linear wave theory. Files with this information are generated at each

radar site and sent to the Ocean Radar Facility together with some additional quality control and

assessment data. These are then packaged into NetCDF files and sent on to the IMOS archive for

access through the data portal.

In the case of SeaSonde data radial currents from the pair of sites are combined at the facility

using CODAR software providing ~1-hour averaged vector current maps. These are transferred

as NetCDF files to IMOS. Basic quality-control

procedures are carried out at this stage to ensure

an acceptable level of data quality.

A similar procedure for the WERA data is carried

out by AODN using their Matlab code. Several

quality control measures are recommended

in the literature and on manufacturer’s

websites when carrying out this procedure.

Technical summary

Surface Currents

Ocean Radar

Ocean radar has two software packages for extracting wave information from the WERA radar

signal.

The basic package provided by the manufacturer, Helzel GmbH, is based on a semi-empirical

method described in. This provides single radar estimates of the wave frequency spectrum from

which significant wave height and dominant period are extracted. These single radar estimates are

calculated at the sites and sent to the Ocean Radar facility where they are packaged into the same

NetCDF files as the currents. The option to combine these files to try to reduce the ambiguities that

are present in single radar data has not yet been implemented

The Seaview Sensing wave measurement

package, which is offered as an option

by Helzel GmbH, is based on methods

described in. The full directional spectrum

and derived parameters, e.g. significant

wave height, peak period and direction,

can be obtained provided the signal to

noise is sufficient. Single radar estimates

can extend the coverage for wave height

and period albeit with some ambiguities.

Technical summary

Waves

Ocean Radar

Wind direction is a parameter that has been measured with HF radars over many years. It is obtained

by taking the ratio of the amplitude two first-order Bragg peaks (the same signal that is used for

current measurement except there we use the frequency of the peaks) and applying a directional

wave model. It is the short wave direction that is being estimated but, in most circumstances, these

waves are expected to be aligned with the wind and hence the direction can be interpreted as wind

direction. For the WERA data, this measurement can be made with the Seaview package which is

currently being implemented. In the meantime, the amplitude of the two peaks is included in the

single radar NetCDF files and the ratio of these can be used to provide qualitative information about

the changing wind directions.

Accurate wind speed estimation is still a research area for HF radar. The Seaview package when

implemented will provide an estimate but it is not expected to be very accurate, particularly in low

wind/swell cases.

Technical summary

Winds

Ocean Radar

Although Australia has a long history in HF radar oceanographic research, this was quite small

in scale and most Australian oceanographic scientists had not been exposed to the benefits of

radar in general or the relative merits of the two technologies. However, now interest is rising,

especially in merging the radar data with models through assimilation, aimed at both improving

model prediction capabilities and radar performances.

The large operational ranges of the HF radar networks (often extending offshore up to 200 km)

allows for the monitoring of the major current systems along the Australian coast and the study of

their spatial and temporal variability, the interaction with mesoscale eddies and the mechanisms

that create these features along with the frequent smaller-scale eddies.

Additional uses include Search and Rescue

activities, prawn and scallop fisheries in the Great

Barrier Reef and tuna fisheries in South Australia.

There is great potential in Australia, and also

a big need particularly in the vulnerable Great

Barrier Reef, to use HF radar for port and harbor

management using both currents and wave

information.

The Ocean Radar Facility is also actively involved

within the Global High-Frequency Network

Component of the Group on Earth Observations

to support further development of HF radar networks and to promote the standardization of data

products and QA/QC methodologies

Technical summary

Application of Data

Ocean Radar

Ocean radar stations have been deployed at six sites around Australia. Two radar stations are

required at each site to produce surface current maps in the area of common overlap.

IMOS has several radar sites located at the Capricorn Bunker Group on the Great Barrier Reef

(Queensland); Coffs Harbour (New South Wales); Bonney Coast and Gulfs (South Australia);

Rottnest Shelf and Turquoise Coast (Western Australia).

Technical summary

Sites

The Capricorn Bunker Group site in

Queensland, is a WERA phased array

system consisting of two stations: TAN:

Tannum Sands, Location: 23.9416°S,

151.3706°E and LEI: Lady Elliot Island,

Location: 24.1113°S, 152.7128°E. The

stations began operation in November

2007. This station support research

around Heron Island and the Capricorn/

Bunker Groups.

Capricorn Bunker

Ocean Radar

Technical summary

Sites

The Coffs Harbour site, in northern New South

Wales, is a WERA phased array system comprised

of two stations: RRK: Red Rock, Location:

29.9839°S, 153.2312°E and NNB: North

Nambucca, Location: 30.624°S, 153.0111°E.

The station began operation in March 2012. This

station aims at observing the East Australian

Current (EAC) characteristics and dynamics of

the shelf, wave spectra, and sediment transport.

Coffs Harbour

The Bonney Coast site, in South Australia, is a

SeaSonde direction finding system consisting

of two stations: NOCR: Nora Creina, Location:

37.3286°S, 139.8498°E and BFCV: Black

Fellows Cave, Location: 37.9395°S, 140.4566°E.

The station began operation in July 2010. This

SeaSonde station was positioned to observe

the coastal upwelling and pulse of the Leeuwin

Current and meteorological fronts approaching

landfall.

Bonney Coast

Ocean Radar

Technical summary

Sites

The South Australia Gulfs site, in central South

Australia, is a WERA phased array system

containing two stations: CSP: Cape Spencer,

Location: 35.2956° S, 136.8826°E and CWI:

Cape Wiles, Location: 34.9428° S, 135.6825°E.

The station began operation in December 2009.

The South Australia Gulf station is located

near the Gulf entrance to examine surface

currents and wave climate in the entrance to

the Spencer Gulf and St Vincent’s Gulf to study

inter-shelf mixing along the eastern shore of the

Great Australian Bight and the Gulfs. Additional

priorities are the progress of meteorological

fronts across the eastern side of the Bight.

South Australia Gulf

The Rottnest Shelf site, in Western Australia, is

a WERA phased array system that includes two

stations: FRE: Fremantle, Location: 32.0314°S,

115.7461°E and GUI: Guilderton, Location:

31.3417°S, 115.4894°E. The station began

operation in March 2010. This station aims to

observe the dynamics of the interaction between

the open ocean and Perth Canyon.

Rottnest Island

Ocean Radar

Technical summary

Sites

The Turquoise Coast site, in Western Australia, is a

SeaSonde direction finding system that has two stations.

The initial installation included CRVT: Cervantes, Location:

30.5065°S, 115.0592°E (until 30 Nov 2012) and SBRD:

Seabird, Location: 31.2811°S, 115.4442°E (until 10 Mar

2013) and the current stations are: GHED: Green Head,

Location: 30.073 °S 114.967 °E (starting on 12 Dec 2012)

and LANC: Lancelin, Location: 31.027 °S 115.329 °E

(starting on 1 Apr 2013). This station was positioned to

support research on meanders of the Leeuwin Current

onto the shelf and dynamics of return flows closer to the

coast.

South Australia Gulf